1. Field of the Invention
The present invention relates to paper feeding control in optionally mounting an automatic paper feeder on a serial printer, etc.
2. Description of the Prior Art
Automatic paper feeders of this type are conventionally well known, each of which is mounted on a printer and feeds paper to a platen of the printer by making use of rotary force of the platen after separating printing media one at a time from a paper feeding mechanism.
Referring to FIG. 4, which illustrates a prior automatic paper feeder mounted on a printer, a paper guide 2 is provided for guiding a printing medium 3 along a platen 1, in close contact with which platen 1 press rollers 4a and 4b travel on the printing medium 3. Top and tail ends of the printing medium 3 are detected by a medium detector 5. A printing head 6 is provided for printing facing to the platen 1 driven by a platen driving motor 7. The automatic paper feeder 8 includes therein a paper feed roller 9 rotated by the platen driving motor 7 via an idle gear 10, a driving belt 11, and an electromagnetic clutch 22 for delivering the printing media 3 one at a time by a housing stacker 13 with the aid of a separating mechanism 14. The printing medium is fed through feed rollers 15a and 15b, discharged after printing, and housed in a discharge stacker 17 through discharge rollers 16a and 16b.
Referring to FIG. 5, which illustrates a control circuit for controlling paper feeding, a processing unit 18 (hereinafter referred to as a CPU) controls all of the control circuit. A read-only nonvolatile memory 19 (hereinafter referred to as a ROM) stores a control program. Designated at 20 is a read/write permit volatile memory (hereinafter referred to as a RAM). The CPU 18, ROM 19, and RAM 20, etc., are interconnected via an input/output bus 21. A driver 23 is provided for driving the head 6, the platen driving motor 7, a carriage driving motor 22, and the electromagnetic clutch 12. In addition, designated at 24 is an I/O port for the automatic paper feeder 8, and element 25 is a connector.
The following is a description of the operation of the automatic paper feeder described above which takes in in the printing medium 3 and finally discharge the medium 3.
With the CPU 18 being supplied with an intake signal issued from an interface circuit (I/F circuit) (not shown), the platen driving motor 7 is driven through the driver 3, while the electromagnetic clutch 12 on the side of the automatic paper feeder 8 is energized. With the electromagnetic clutch 12 so energized, the paper feed roller 9 is rotated via the idle gear 10 and the driving belt 11, whereby the printing media 3 are separated off one at a time with the aid of the separating mechanism 14 and forced to travel through the feed rollers 15a and 15b.
The medium detector 5 detects the top end 3a of the printing medium and informs the CPU 18 of this fact. Thereafter, with the passage of a prescribed period of time, the CPU 18 turns the electromagnetic clutch 12 off so as to stop the paper feed roller 9. The the printing medium 3 forced to travel by the feed rollers 15a and 15b, is held along the paper guide 2 between the platen 1 and the press rollers 4a and 4b. The platen driving motor 7, after the detection of the top end 3a of the medium 3 by the medium detector 5, is driven corresponding to a prescribed amount of heading of the printing medium 3 as stored in the control program, and is thereafter stopped by the CPU 18 to finish the heading of the printing medium 3.
The above arrangement however suffers from some drawbacks. Namely, there is a long travel distance of the printing medium from the medium detector 5 to a position where the heading of the printing medium is finished. Accordingly, if there are any frictional losses, any errors of mounting of the medium detector 5 and the like, then the heading position of the printing medium 3 is displaced even if the platen driving motor 7 is driven by a prescribed amount.